The objective of the present proposal is to define the role of calcium in the control of renal hemodynamics, the secretion of renin and water homeostasis. To this end extensive use of agents that promote as well as inhibit cellular calcium uptake will be undertaken. The role of cellular calcium uptake in the control of renal blood flow will be investigated in anesthetized animals by employing physiologic and pharmacologic maneuvers that either vasodilate or vasoconstrict the renal circulation. Effects on glomerular filtration will be concomitantly monitored and complemented by studies on the cyclic AMP and cyclic GMP system in isolated glomeruli. The possible role of cellular calcium uptake on renin secretion will also be investigated in the dog by testing the effect of calcium and the above agents in maneuvers that are known to enhance and inhibit renin release. A possible relationship to the prostaglandin system will be studied. The effects of calcium on water homeostasis will involve studies on both the release and action of antidiuretic hormone. Intraventricular injections in the rat, accompanied by monitoring of renal and systemic hemodynamics, renal water excretion and immunoassayable antidiuretic hormone levels will be undertaken to study the central mechanisms. Investigations of the renal response to vasopressin will be accompanied by studies of cyclic nucleotides in medullary papillary region as well as in isolated antidiuretic hormone responsive tubular segments.